3,4-dihydro-3//-pyrrol-2-imines as conformationally restrained 1,3-diazabutadienes: Synthesis, structural properties and profanation

Article abstract of DOI:10.1002/ejoc.200900045

5-Aryl-3,3,4,4-tetramethyl-3,4-dihydro-3H-pyrrol-2-imines, conformationally restrained 1,3-diazabuta-1,3-diene derivatives, were easily prepared by treating aryllithium species with 2,2,3,3-tetramethylsuccinonitrile (1). Trapping the reaction intermediate

Full text of DOI:10.1002/ejoc.200900045

FULL PAPER
DOI: 10.1002/ejoc.200900045
3,4-Dihydro-3H-pyrrol-2-imines as Conformationally Restrained
1,3-Diazabutadienes: Synthesis, Structural Properties and Protonation[‡]
Simon Janich,[a] Roland Fröhlich,[a] Andrea Wilken,[a] Jan von Zamory,[a]
Atsushi Wakamiya,[b] Shigehiro Yamaguchi,[b] and Ernst-Ulrich Würthwein*[a]
Keywords: Nitrogen heterocycles / Cross-coupling / Acidity / Fluorescence
5-Aryl-3,3,4,4-tetramethyl-3,4-dihydro-3H-pyrrol-2-imines,
conformationally restrained 1,3-diazabuta-1,3-diene deriva-
tives, were easily prepared by treating aryllithium species
with 2,2,3,3-tetramethylsuccinonitrile (1). Trapping the reac-
tion intermediate with chlorotrimethylsilane gave N-silylated
to obtain N-arylated compounds 5b–h,j,k,m and 7a–d. The
UV spectra of compounds 5 and 7 exhibit long wavelength
absorptions up to 462 nm for 7d, thus indicating extended π–
π* conjugation. Dihydropyrrolimine-based compounds with
larger conjugated aryl substituents in the 5-position react
compounds 2a–e, whereas aqueous workup gave N-H deriv- with Brønsted and Lewis acids displaying a significant colour
atives 3a,b. Pyrenyl-substituted compound 3b was character-
ised by X-ray diffraction studies, revealing the presence of
both intermolecular aromatic face-to-face contacts and the
formation of homodimers by twofold H-bonding. N-Silylated
change that could be used to estimate the pKb of 3a to a
value of –4.5. Derivatives 2c,e and 3a,b, which are not N-
arylated, are fluorescent with a Stokes shift of 107 nm
(6034 cm–1) for 3a.
derivatives 2a–d were used successfully as nucleophilic com- (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim,
ponents in palladium-catalysed C–N bond-forming reactions
Germany, 2009)
oligonitriles, such as absorptions in the UV/Vis spectra at
longer wavelengths, indicating the presence of larger chro-
mophores due to the extended conjugation. Replacing the
terminal amino group with an aryl moiety leads to confor-
mationally restrained 1,3-diazabuta-1,3-diene derivatives
that can form extended conjugated systems spreading over
both the aromatic part and the heteropolyene chain. As a
result of the asymmetric substitution of the dihydropyrrole
subunit, these building blocks have a distinct dipole mo-
ment pointing roughly in the direction of the exocyclic
imino moiety. Exploiting this feature by choosing an elec-
tron-donating group for the 5-position and attaching an
electron-poor moiety at the imino nitrogen atom could give
rise to interesting optical properties by an intramolecular
charge transfer along the molecule backbone (Figure 1).
Introduction
1,3-Diazabuta-1,3-dienes can be regarded as nitrogen-
rich analogues of buta-1,3-dienes. They contain an amidine
subunit, thus forming a backbone of alternating C–N
double and single bonds. Unlike the 1,3-butadienes, 1,3-di-
azabuta-1,3-dienes as other oligonitriles[1,2] have a low ener-
getic barrier for rotations about the central C–N single
bond, which leads to high structural flexibility.[3,4,5] In ad-
dition, they prefer a three-dimensionally twisted structure
due to n–π interactions between the lone pairs at the nitro-
gen atoms and the neighbouring double bonds. Thus, in
contrast to polyenes, no continuous conjugation along the
molecule backbone is observed.
Recently, we reported on the synthesis of oligonitrile de-
rivatives with conformationally restrained (5-imino-4,5-di-
hydro-3H-pyrrol-2-yl)amine subunits as planarised 1,3,5-
triazapenta-1,3-diene moieties.[12] Unlike their open-
chained counterparts, the N–C–N–C–N backbone is fixed
in a W shape conformation, thus leading to π–π* conjuga-
tion of the two consecutive C–N double bonds. This results
in properties that differ considerably from the open-chained
[‡] Unsaturated Hetero Chains, XVIII. Part XVII: Ref.[1]
[a] Organisch-Chemisches Institut, Westfälische Wilhelms-Uni-
versität,
Figure 1. Schematic presentation of the donor–acceptor substituted
1,3-diazabuta-1,3-diene system with the dipole vector.
Corrensstraße 40, 48149 Münster, Germany
Fax: +49-251-83-39772
E-mail: wurthwe@uni-muenster.de
[b] Department of Chemistry, Graduate School of Science, Nagoya
University,
For the synthesis of conformationally restrained 1,3-diaza-
buta-1,3-diene derivatives, we employed a anionic cycli-
sation reaction that is known for the synthesis of heterocyclic
Nagoya 464-8602, Japan
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E.-U. Würthwein et al.
FULL PAPER
compounds from 1,2- or 1,3-dinitriles. Linstead and Elvidge
Reactions with 2-bromothiophene as starting material
described the preparation of succinimidine by heating suc- give the unusual bis-dihydropyrrolimine 2e as the main
cinonitrile with a methanol solution of ammonia under product. It appears that the proton in the 5-position of the
pressure.[6] Scheffold and his coworkers synthesised dihy- thiophene is acidic enough to be abstracted by the basic
dropyrrolimine derivatives by treating nucleophilic methyl lithiated intermediate, thus creating a second nucleophilic
species with tetramethylsuccinonitrile.[7] The same reaction site that reacts with another equivalent of dinitrile 1
mechanism can be found in polymer science, such as intra- (Scheme 2).
molecular anionic cyclisations in polyacrylonitriles[8,9] or
the synthesis of polynitriles from succinonitrile and fuma-
ronitrile, as studied by Wöhrle.[10,11]
In this report, we describe the synthesis of conformation-
ally restrained 1,3-diazabuta-1,3-dienes and their use as nu-
cleophilic components in palladium-catalysed C–N bond-
formation reactions. Furthermore, we report on the optical
and structural properties of these compounds as studied by
UV/Vis and fluorescence spectroscopy and by X-ray dif-
fraction.
Results and Discussion
The procedure for the synthesis of the N-silylated 5-aryl-
dihydropyrrol-2-imines was adapted from the protocol used
by Marihart, Greving et al. to synthesise conformationally
restrained 1,3,5-triazapenta-1,3-diene building blocks for
oligonitriles,[12]which in turn is based on a procedure pub-
lished by Wöhrle.[11] The employed 2,2,3,3-tetramethylsuc-
cinonitrile (1) is easily available by controlled decomposi-
tion of azoisobutyronitrile (AIBN).[13] This tetramethyl-
substituted dinitrile is nonenolisable, which is advantageous
for the reactions reported here. The synthesis starts with
the transformation of an aryl bromide into the nucleophilic
aryllithium compound by a metal–halogen exchange with
n-butyllithium at –78 °C. To this, a solution of a slight ex-
cess of dinitrile 1 is added. After warming to 0 °C and stir-
ring for 30 min, the solution is cooled to –78 °C again, and
the lithiated intermediate is trapped by adding chlorotri-
methylsilane to give N-silylated compounds 2. Aqueous
workup instead of quenching with TMSCl results in unpro-
tected compounds 3 (Scheme 1).
Scheme 2.
Compounds 2 and 3 were completely characterised by
spectroscopic methods. Bis-dihydropyrrolimine 2e exhibits
1
clear indications in the H NMR spectrum of two isomeric
forms in a 5:1 ratio, probably conformers regarding the ori-
entation of the dihydropyrrole moieties relative to the cen-
tral thiophene unit and to each other. Pyrenyl-substituted
derivative 3b could also be characterised in the solid state
by X-ray structure determination. The packing structure of
this compound is governed by face-to-face aromatic interac-
tions between the pyrenyl groups that are 3.456 Å apart and
by NH···N interactions between the terminal imino moie-
ties and the dihydropyrrole nitrogen atoms forming a
homodimeric structure with two equivalent H-bonds. How-
ever, these interactions do not seem to be very strong, as the
Scheme 1.
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N–N distances are 3.320 Å with N–H distances of 2.428 Å
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Conformationally Restrained 1,3-Diazabutadienes
(Figure 2). Our earlier examples of such homodimers dis-
played N–N distances from 2.919 to 2.988 Å.[12] The pyr-
enyl moiety is significantly tilted relative to the dihydropyr-
role ring, as illustrated by the torsion angle C1a–Cipso–C–N
(70.35°).
Scheme 3.
Table 1. Screening of catalysts and reaction conditions for the reac-
tion of 2a with 4a to give 5b.
Entry
Pd source
Ligand
Conditions
Yield [%]
1
2
3
4
5
6
Pd2(dba)3
Pd2(dba)3
Pd2(dba)3
Pd2(dba)3
Pd(OAc)2
Pd(OAc)2
P(o-Tol)3
P(tBu)3
90 °C, 17 h
90 °C, 17 h
0
3
43
57
43
8
S-Phos[19,20] 90 °C, 17 h
rac-BINAP
rac-BINAP
rac-BINAP
90 °C, 17 h
90 °C, 4 h
r.t., 17 h
Scheme 4.
Table 2. Substitution pattern of compounds 2, 4 and 5 and yields
of N-arylated-5-aryldihydropyrrol-2-imines 5.
5
2
Ar
4
ArЈ
X
Yield
[%]
a
b
c
d
e
e
a
c
Thiophen-2,5-diyl
5-TIPS-thiophen-2-yl
4-(Ph)Ph
a
a
a
a
a
b
c
d
e
f
g
h
i
j
k
l
4-(CF3)Ph
4-(CF3)Ph
4-(CF3)Ph
4-(CF3)Ph
4-(CF3)Ph
4-BrPh
Br
Br
Br
Br
Br
I
I
Br
I
Br
Br
Br
Br
Br
0
57
62
65
67
72
73
36
0
52
25
0
16
0
Figure 2. Molecular structure of 3b in the crystalline state as ob-
tained by X-ray diffraction. Top: single molecule (PLATON
plot14); bottom: ensemble of three molecules exhibiting face-to-face
aromatic interactions on the left-hand side and long NH···N inter-
actions between the middle and the right-hand molecule (MER-
CURY plot [15]).
d
b
b
b
b
b
b
b
b
b
b
b
b
Pyren-1-yl
4-(NPh2)Ph
4-(NPh2)Ph
4-(NPh2)Ph
4-(NPh2)Ph
4-(NPh2)Ph
4-(NPh2)Ph
4-(NPh2)Ph
4-(NPh2)Ph
4-(NPh2)Ph
4-(NPh2)Ph
4-(NPh2)Ph
4-(NPh2)Ph
f
g
h
i
j
k
l
m
n
o[a]
p[b]
2-BrPh
2,4,6-(CH3)Ph
2,6-(iPr)Ph
4-(Ph)Ph
4-(NPh2)Ph
Pyridin-2-yl
Pyridin-3-yl
Pyrimidin-2-yl
(N-Boc)-pyrrol-2-yl Br
5-Phenyl-
(N-Boc)-pyrrol-2-yl
3,4,5-Triphenyl-
(N-Boc)-pyrrol-2-yl
In order to obtain dihydropyrrolimines bearing an ad-
ditional aryl substituent at the imine moiety, N-silylated
compounds 2 were employed as nucleophiles in a Buch-
wald–Hartwig-type palladium-catalysed cross-coupling re-
action with aryl halides 4.[16–21] The most suitable catalyst
system and reaction conditions were determined by a series
of test reactions with dihydropyrrolimine 2a as the nucleo-
phile and 1-bromo-4-(trifluoromethyl)benzene (4a) as the
electrophilic component (Scheme 3, Table 1).
0
0
Br
q[a]
b
4-(NPh2)Ph
m
Br
0
Because the employed palladium source hardly affected
the outcome of the reaction, a catalyst system consisting of
the cheaper and less-sensitive palladium(II)acetate and rac-
[a] K3PO4 as base. [b] Cs2CO3 as base.
BINAP was chosen for the following syntheses of a variety slightly sterically hindered electrophiles like 2-bromomesity-
of N-arylated dihydropyrrolimines 5 (Scheme 4, Table 2). lene (4d) and 1-bromo-2-iodobenzene (4c) could be used
The employed N-silylated dihydropyrrolimine barely af- without problems in this reaction. In contrast, more steri-
fected the outcome of the reaction, and only bis-dihydro- cally hindered aryl halides like 2,6-diisopropyl bromoben-
pyrrolimine 2e did not react. A possible reason for this zene (4e) and the N-Boc-protected 2-bromo-3,4,5-tri-
could be deactivation of the catalyst by the compound. phenylpyrrole 4m did not react at all under the employed
Both electron-rich and electron-poor aryl halides and even conditions. Reactions with 2-azaaryl halides like 2-bromo-
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E.-U. Würthwein et al.
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pyridine (4h), 2-bromopyrimidine (4j) and the less-hindered ond substitution to produce 7e completely. A threefold
2-bromopyrrole derivatives (4k,l) always gave complex mix- coupling reaction at 1,3,5-tribromobenzene 6e to give com-
tures of products that showed no trace of the desired prod- pounds like 7f,g is probably prevented by the substantial
ucts.
steric demand of the dihydropyrrolimino substituents.
By using the same conditions as above, the synthesis of
Obtained compounds 5 and 7 were completely character-
several branched N-arylated dihydropyrrolimines (7) based ised by spectroscopic methods, compounds 5b and 5k ad-
on symmetric aryl di- or trihalides (6) was attempted ditionally by X-ray structure analysis. Both compounds
(Table 3, Scheme 5).
share common characteristics in the solid state: the aryl
moiety in the 5-position of the dihydropyrrole ring is nearly
coplanar to the dihydropyrrole ring itself, the iminic double
bond is Z configured and the aryl substituent at the imine
nitrogen atom is twisted out of plane (Figure 3). This is
illustrated by the corresponding dihedral angles along the
S–C–C–N–C–N–Cipso–Cortho backbone of 5b (–18.66,
177.16, 167.58, –3.63 and –64.12°) and the dihedral angles
along the Cortho–Cipso–C–N–C–N–Cipso–Cortho backbone of
5k (from the 5-aryl substituent to the aryl moiety at the
imine nitrogen; –9.61, 177.57, 164.32, 7.18 and 34.99°).
Table 3. Substitution pattern of compounds 2, 6 and 7 and yields
of branched N-arylated-5-aryldihydropyrrol-2-imines 7.
7
2
Ar
6
ArЈXn
Yield [%]
a
b
c
d
e
f
b
c
c
b
b
c
b
4-(NPh2)Ph
4-(Ph)Ph
4-(Ph)Ph
4-(NPh2)Ph
4-(NPh2)Ph
4-(Ph)Ph
a
b
c
c
d
e
e
1,4-diiodobenzene
25
3
2,5-dibromothiophene
4,4Ј-dibromobiphenyl
4,4Ј-dibromobiphenyl
2,7-dibromofluorene
1,3,5-tribromobenzene
1,3,5-tribromobenzene
21
31
0[a]
0[b]
0[b]
g
4-(NPh2)Ph
[a] Only monosubstituted product. [b] Only mono- and disubsti-
tuted products.
Scheme 5.
Figure 3. Molecular structures of 5b (top) and 5k (bottom) in the
crystalline state as obtained by X-ray diffraction (PLATON
plots,[14] hydrogen atoms omitted for clarity).
The lower yields obtained throughout are likely to be a
result of an increase in the electron density in the electro-
phile after the attachment of the first strongly electron-do-
nating dihydropyrrole moiety, resulting in deactivation of
The UV/Vis spectra show clear indications of extended
the aryl halide towards further coupling reactions. In the π–π* conjugation of the aryl substituents in the 5-position
case of 2,7-dibromofluorene 6d, which is already electron and the dihydropyrrole moiety. The longest wavelength ab-
rich by itself, this deactivation is sufficient to prevent a sec- sorptions range from 374 to 462 nm for 5b and 7d, respec-
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Conformationally Restrained 1,3-Diazabutadienes
tively, depending on the size and electronic properties of the whole backbone of the molecule, and which bears similari-
aryl substituents and the overall extent of the conjugated ties to the well-known cyanine dyes. This interpretation is
system, resulting in intense yellow to red hues. In the case well supported by quantum chemical DFT calculations
of derivatives of 5 and 7 with larger aryl groups in the 5- [B3LYP/6-311+G(2d,p)],[22] which give a HOMO/LUMO
position, such as pyrenyl or 4-(N,N-diphenylamino)phenyl gap of 3.56 (3a) and 3.37 eV (3b) for the nonprotonated
moieties, the compounds show a significant colour change species, but a much smaller gap of 2.75 eV (3a+H+) and
upon treatment with Brønsted or Lewis acids (Scheme 6, 2.53 eV (3b+H+) for the N-protonated forms.
Figure 4). Figure 4 shows the colour change in a THF solu-
Compounds 3a and 3b and their N-silylated derivatives
tion of 3a upon addition of trifluoromethanesulfonic acid 2c and 2e are fluorescent under irradiation with UV light.
and a corresponding series of UV/Vis spectra recorded with In the fluorescence spectrum of 3a, a single emission band
increasing amounts of the acid. Quantitative evaluation of with a maximum at 478 nm is visible (Figure 5, top). The
these spectra allows the pKB value of the protonation reac- Stokes shift is 6034 cm–1 (107 nm). The absorption spec-
tion to be determined as roughly –4.5, thus underlining the trum of pyrenyl-substituted compound 3b is very much sim-
basicity of the dihydropyrrolimines. The colour change is ilar to the corresponding spectrum of pyrene.[23] The emis-
fully reversible by addition of a base, such as triethylamine. sion spectrum, in contrast, differs significantly: Whereas the
A crystal structure of a hydro iodide of a related 5-amino- less-intense and sharp bands at 383 and 397 nm can be con-
dihydropyrrolimine obtained by Marihart[12] shows proton- tributed to emissions of the pyrene moiety, the strong band
ation at the exocyclic imino nitrogen atom. In the case of a with a maximum at 432 nm and a shoulder at roughly
5-aryldihydropyrrolimine, this could lead to structure 450 nm seem to be the result of the influence of the DHPI
3+H+, in which the positive charge is delocalised along the substituent (Figure 5, bottom). The Stokes shift between
the last sharp absorption band and the first emission
band – both associated to the pyrene moiety – is 3049 cm–1
(40 nm). In the N-arylated derivatives of these compounds
the excitation necessary for fluorescence appears to be re-
laxed on nonradiative pathways, probably by rotation of the
highly flexible aryl moiety at the imino function.
Scheme 6.
Figure 4. Colour change in a THF solution of 3a upon addition of
trifluoromethanesulfonic acid.
Figure 5. Absorption and emission spectra of 3a (top) and 3b (bot-
tom) (fluorescence spectra: THF, c = 10–6 ).
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5.0 mmol), 1 (0.68 g, 5.0 mmol) and chlorotrimethylsilane (0.7 mL,
Conclusions
0.60 g, 5.5 mmol). Yield: 1.66 g (3.7 mmol, 74%), yellow oil, b.p.
1
We have described the synthesis of 5-aryl-3,4-dihydropyr-
rol-2-imines by reaction of aryllithium species with 2,2,3,3-
tetramethylsuccinonitrile 1. Trapping lithiated intermediate
2-Li with chlorotrimethylsilane yields N-silylated com-
pounds 2a–e, whereas aqueous workup gives unprotected
derivatives 3a,b. N-Silylated compounds 2 were employed
as nucleophiles in palladium-catalysed cross-coupling reac-
tions to obtain N-arylated compounds 5 and the corre-
sponding bis-armed derivatives 7. Conformation and con-
figuration in the solid state were determined by X-ray dif-
fraction studies of 3b, 5b and 5k.
The optical properties of the obtained products with the
longest wavelength absorptions of up to 462 nm for
branched compound 7d are regarded as clear indications of
π–π* conjugation between the aryl groups and the plan-
arised azapolyene substructure. Derivatives with large con-
jugated aryl substituents in the 5-position react to Brønsted
and Lewis acids with a substantial colour change. Deriva-
tives that are not N-arylated, 2c,e and 3a,b, in addition
show intense fluorescence with Stokes shifts of 6034 and
3049 cm–1 for 3a and 3b, respectively.
156 °C (0.08 Torr). H NMR (400.13 MHz, CDCl3): δ = 0.26 (s, 9
H, SiCH3), 1.05 (s, 6 H, CH3), 1.12 (d, 3J = 7.5 Hz, 18 H, iPrCH3),
3
3
1.31 (s, 6 H), 7.28 (d, J = 3.7 Hz, 2 H), 7.83 (d, J = 3.7 Hz, 2 H,
CHthioph.) ppm. 13C NMR (100.61 MHz, CDCl3): δ = 1.4 (SiCH3),
2.1, 11.9 (SiCH), 18.7 [SiCH(CH3)2], 22.9, 23.7 (CH3), 50.1, 52.6
(Cquat.), 125.2, 132.1, 136.4 (Carom.), 149.0 (Cipso), 183.4, 184.8
(C=N) ppm. IR: ν = 2965 (m), 2945 (m), 2893 (w), 2866 (m), 2361
˜
(w), 2342 (w), 1693 (s), 1543 (vs), 1506 (m), 1499 (m), 1460 (m),
1425 (w), 1391 (w), 1375 (w), 1368 (m), 1327 (w), 1281 (w), 1265
(w), 1242 (s), 1200 (w), 1161 (w), 1146 (w), 1090 (m), 1074 (m),
1016 (m), 999 (m), 980 (m), 907 (m), 881 (vs), 837 (s), 829 (vs), 804
(m), 762 (m), 750 (m), 727 (w), 710 (w), 685 (s), 656 (vs), 642 (vs),
633 (vs), 606 (m), 596 (m), 584 (m), 565 (s) cm–1. MS-ESI-EM:
calcd. for [M – TMS + H]+ 377.2441; found 377.2436.
C24H44N2SSi2 (448.86): calcd. C 64.22, H 9.88, N 6.24; found C
64.01, H 9.86, N 6.27.
N-Phenyl-N-{4-[3,3,4,4-tetramethyl-5-(trimethylsilylimino)-4,5-dihy-
dro-3H-pyrrol-2-yl]phenyl}benzenamine (2b): From of 4-bromo-
N,N-diphenylbenzenamine (3.24 g, 10.0 mmol), n-butyllithium
(6.25 mL, 10.0 mmol), 1 (1.50 g, 11.0 mmol) and chlorotrimethyl-
silane (1.4 mL, 1.20 g, 11.0 mmol). Yield: 2.60 g (5.7 mmol, 57%),
bright yellow glasslike solid, b.p. 221 °C (2.8 ϫ 10–2 mbar). 1H
NMR (399.65 MHz, CDCl3): δ = 0.25 (s, 9 H, SiCH3), 1.04 (s, 6
3
H, CH3), 1.28 (s, 6 H), 7.02 (d, J = 8.8 Hz, 2 H), 7.10–7.18 (m, 7
3
H), 7.30–7.34 (m, 4 H), 7.91 (d, J = 8.8 Hz, 2 H, CHarom.) ppm.
Experimental Section
13C NMR (100.40 MHz, CDCl3): δ = 1.4 (SiCH3), 22.7, 23.7 (CH3),
50.7, 52.6 (Cquat.), 120.4, 124.5, 125.9, 129.7, 130.9 (Carom.), 146.7,
Materials and Methods: IR: Nicolet 5DXC. 1H NMR: Bruker WM
300 (300.13 MHz), JEOL AL-400 (399.65 MHz), Bruker AMX 400
(400.13 MHz), Varian INOVA 500 (499.8 MHz) and Varian Unity
600 (599.86 MHz); internal reference tetramethylsilane. 13C NMR:
Bruker WM 300 (75.47 MHz), JEOL AL-400 (100.40 MHz),
Bruker AMX 400 (100.61 MHz), Varian INOVA 500 (125.7 MHz)
and Varian Unity 600 (150.84 MHz); internal reference solvent.
MS-ESI-EM: Bruker MicroTOF. UV/Vis: Shimadzu UV-3150,
Varian Cary 1 Bio. Fluorescence: Aminco-Bowman Series 2. CHN
elemental analysis: Elementar Vario El III. Melting points are un-
corrected. All solvents were rigorously dried by standard methods.
When necessary, the experiments were carried out with complete
exclusion of moisture (argon, septum–syringe technique) in glass-
ware that had been thoroughly dried by repeated heating under an
atmosphere of argon and subsequent evacuation. Column
chromatography: Silica gel Merck 60 (0.040–0.063 mm). TLC:
Merck silica gel plates (silica gel 60 F254); detection with UV light.
151.0 (Cipso), 184.0, 190.0 (C=N) ppm. IR: ν = 3061 (w), 3038 (w),
˜
2970 (w), 2930 (w), 2361 (w), 2340 (vw), 1663 (m), 1609 (w), 1587
(s), 1564 (m), 1524 (m), 1508 (s), 1489 (s), 1450 (w), 1422 (m), 1395
(m), 1379 (w), 1369 (w), 1325 (s), 1294 (s), 1285 (s), 1271 (s), 1248
(m), 1219 (m), 1192 (m), 1182 (m), 1161 (w), 1144 (m), 1123 (m),
1096 (m), 1074 (m), 1028 (w), 968 (w), 889 (s), 833 (s), 748 (s), 718
(w), 694 (vs), 664 (w), 637 (w), 621 (m), 569 (w) cm–1. MS-ESI-
EM: calcd. for [M – TMS + H]+ 382.2278; found 382.2278. UV/
Vis (THF): λ (ν, cm–1; ε, –1 cm–1) = 371 (26954, 24000), 296
˜
(33783, 19600) nm.
5-Biphenyl-3,3,4,4-tetramethyl-N-(trimethylsilyl)-3,4-dihydropyrrol-
2-imine (2c): From 4-bromobiphenyl (2.33 g, 10.0 mmol), n-butyl-
lithium (6.25 mL, 10.0 mol), 1 (1.50 g, 11.0 mmol) and chlorotri-
methylsilane (1.4 mL, 1.20 g, 11.0 mmol). Yield: 1.79 g (4.9 mmol,
49 %), yellow solid, b.p. 156 °C (2.5 ϫ 10–2 mbar). 1H NMR
(300.14 MHz, CDCl3): δ = 0.22 (s, 9 H, SiCH3), 1.00 (s, 6 H, CH3),
1.23 (s, 6 H, CH3), 7.31–7.42 (m, 2 H), 7.55–7.61 (m, 5 H), 8.00 (d,
3J = 8.4 Hz, 2 H, CHarom.) ppm. 13C NMR (75.47 MHz, CDCl3): δ
= 1.4 (SiCH3), 22.7 (CH3), 23.4 (CH3), 50.6 (Cquat.), 52.9 (Cquat.),
127.2, 127.2, 127.3, 128.1, 129.0, 129.7, 129.9 (Carom.), 132.9, 140.2,
General Procedure for the Synthesis of Compounds 2a–e: The aryl
halide (10.0 mmol) was dissolved in anhydrous THF (10.0 mL) in
a Schlenk flask that had been dried and then flushed with argon.
The solution was cooled down to –78 °C and n-butyllithium (1.6 
in n-hexane, 6.9 mL, 11.0 mmol) was added. After stirring for 1 h
at –78 °C, 2,2,3,3-tetramethylsuccinonitrile (1; 1.50 g, 11.0 mmol)
dissolved in anhydrous THF (10.0 mL) was slowly added. The reac-
tion mixture was stirred at –78 °C for 30 min, warmed to 0 °C and
stirred for an additional 30 min. Then the solution was cooled
down to –78 °C again and chlorotrimethylsilane (1.20 g, 1.4 mL,
11.0 mmol) was added. The reaction mixture was slowly warmed
to room temperature and stirred for 1 h. The crude product was
obtained by removing the solvent under vacuum and subsequently
purified by Kugelrohr distillation.
144.1 (Cipso), 183.3, 190.8 (C=N) ppm. IR: ν = 3032 (vw), 2974
˜
(m), 2926 (w), 2903 (w), 2872 (vw), 2361 (vw), 2326 (vw), 1707 (s),
1672 (w), 1607 (w), 1566 (m), 1533 (s), 1487 (w), 1472 (w), 1460
(w), 1447 (w), 1404 (w), 1391 (m), 1377 (w), 1369 (w), 1358 (w),
1314 (m), 1302 (m), 1285 (w), 1267 (m), 1238 (m), 1196 (w), 1165
(w), 1144 (m), 1123 (w), 1084 (s), 1040 (w), 1024 (w), 1009 (m), 997
(w), 926 (w), 895 (s), 847 (s), 826 (vs), 770 (s), 750 (m), 737 (vs),
714 (m), 694 (s), 658 (w), 635 (w), 627 (w), 604 (w) cm–1. MS-ESI-
EM: calcd. for [M – TMS + H]+ calcd. 291.1856; found 291.1851.
3,3,4,4-Tetramethyl-5-(pyren-1-yl)-N-(trimethylsilyl)-3,4-dihydro-
pyrrol-2-imine (2d): From 1-bromopyrene (385 mg, 1.4 mmol), n-
butyllithium (0.94 mL, 1.4 mmol), 1 (205 mg, 1.5 mmol) and chlo-
rotrimethylsilane (0.2 mL, 164 mg, 1.5 mmol). Yield: 357 mg
3,3,4,4-Tetramethyl-5-[5-(triisopropylsilyl)thiophen-2-yl]-N-(trimeth-
ylsilyl)-3,4-dihydropyrrol-2-imine (2a): From 2-bromo-5-(triisopro-
pylsilyl)thiophene (1.60 g, 5.0 mmol), of n-butyllithium (3.13 mL,
2082
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© 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Org. Chem. 2009, 2077–2087

Conformationally Restrained 1,3-Diazabutadienes
(0.9 mmol, 62 %), yellow crystalline solid, b.p. 211 °C
(1.9ϫ10–2 mbar). 1H NMR (400.13 MHz, CDCl3): δ = 0.44 (s, 9
H, SiCH3), 1.23 (s, 6 H, CH3), 1.38 (s, 6 H, CH3), 7.99–8.26 (m, 9
= 3063 (w), 3036 (w), 2968 (w), 2926 (w), 2868 (w), 2361 (w), 1666
(m), 1639 (m), 1587 (s), 1566 (m), 1530 (m), 1487 (s), 1450 (m),
1393 (m), 1377 (m), 1368 (m), 1325 (s), 1314 (s), 1277 (s), 1221 (m),
H, CHarom.) ppm. 13C NMR (100.61 MHz, CDCl3): δ = 2.1 1192 (m), 1179 (m), 1142 (m), 1117 (m), 1074 (m), 1051 (m), 1030
(SiCH3), 22.7 (CH3), 23.4 (CH3), 48.6 (Cquat.), 54.7 (Cquat.), 128.5,
(m), 997 (w), 961 (m), 920 (w), 891 (m), 839 (m), 797 (w), 752 (s),
128.6, 128.7, 129.0, 129.3, 129.4, 129.9 (Carom.), 131.8 (Cipso), 186.4, 694 (vs), 669 (m), 637 (m), 623 (m), 563 (m), 554 (m), 532 (m), 523
192.3 (C=N) ppm. IR: ν = 3211 (w), 3038 (w), 2967 (m), 2897 (w),
(s), 517 (s), 511 (s) cm–1. MS-ESI-EM: calcd. for [M + H]+
˜
2868 (w), 2361 (w), 2344 (w), 1717 (w), 1686 (m), 1676 (m), 1653 382.2278; found 382.2295. UV/Vis (THF): λ (ν, cm–1; ε, –1 cm–1)
˜
(w), 1599 (w), 1572 (s), 1539 (w), 1508 (w), 1497 (w), 1489 (w), = 371 (26954, 17800), 297 (33670, 14200) nm. Fluorescence (THF,
1476 (w), 1458 (m), 1445 (w), 1418 (w), 1391 (m), 1375 (w), 1366 c = 10–6 ): λ (ν, cm–1) = 478 (20921) nm.
˜
(m), 1327 (m), 1304 (w), 1265 (m), 1244 (m), 1221 (w), 1196 (w),
3,3,4,4-Tetramethyl-5-(pyren-1-yl)-3,4-dihydropyrrol-2-imine (3b):
1180 (w), 1167 (w), 1159 (w), 1152 (w), 1138 (w), 1124 (w), 1109
(m), 1086 (s), 1051 (m), 1009 (w), 959 (w), 930 (w), 885 (s), 843
(vs), 833 (vs), 772 (m), 756 (s), 746 (m), 735 (m), 721 (m), 708 (s),
691 (m), 681 (m), 664 (w), 640 (m), 617 (w), 606 (w), 588 (w), 579
(w) cm–1. MS-ESI-EM: calcd. for [M – TMS + H]+ 339.1851; found
339.1851.
From 1-bromopyrene (1.00 g, 3.6 mmol), n-butyllithium (2.40 mL,
4.0 mmol) and 1 (0.53 g, 4.0 mmol). Yield: 0.58 g (2.7 mmol, 75%),
yellow crystalline solid, m.p. 193 °C. 1H NMR (400.13 MHz,
CDCl3): δ = 1.21 (s, 6 H, CH3), 1.38 (s, 6 H, CH3), 7.97–8.25 (m,
9 H, CHarom.), 9.00 (br. s, 1 H, NH) ppm. 13C NMR (100.61 MHz,
CDCl3): δ = 22.5 (CH3), 23.2 (CH3), 47.3 (Cquat.), 57.2 (Cquat.),
123.7, 124.4, 124.4, 124.7, 125.6, 125.9, 126.4, 127.1, 128.4, 128.7,
129.2 (Carom.), 130.6, 131.1, 132.1 (Cipso), 187.3, 195.1 (C=N) ppm.
3,3,4,4-Tetramethyl-5-{5-[3,3,4,4-tetramethyl-5-(trimethylsilyl-
imino)-4,5-dihydro-3H-pyrrol-2-yl]thiophen-2-yl}-N-(trimethylsilyl)-
3,4-dihydropyrrol-2-imine (2e): From 2-bromothiophene (1.81 g,
7.5 mmol), n-butyllithium (9.4 mL, 15.0 mmol), 1 (2.04 g, 15 mmol)
and chlorotrimethylsilane (1.9 mL, 1.63 g, 15 mmol). Yield: 0.96 g
(1.6 mmol, 26%), yellow solid, b.p. 196 °C (0.12 Torr). 1H NMR
(300.13 MHz, CDCl3): δ = 0.25 (s, 18 H, SiCH3), 1.05 (s, 10 H),
1.18 (s, 2 H), 1.30 (s, 10 H), 1.34 (s, 2 H, CH3), 7.23 (s, 1.5 H), 7.77
(s, 0.5 H, CHarom.) ppm. 13C NMR (75.47 MHz, CDCl3): δ = 1.3
(SiCH3), 22.7 (CH3), 23.4 (CH3), 50.3 (Cquat.), 52.6 (Cquat.), 131.6
IR: ν = 3211 (w), 3042 (w), 2967 (m), 2922 (m), 2868 (w), 2851
˜
(w), 1674 (m), 1578 (s), 1560 (m), 1539 (m), 1506 (w), 1487 (w),
1476 (m), 1458 (m), 1437 (w), 1393 (m), 1377 (m), 1368 (m), 1325
(s), 1290 (w), 1273 (m), 1244 (m), 1219 (m), 1192 (m), 1180 (w),
1157 (w), 1138 (w), 1107 (m), 1076 (m), 1049 (m), 957 (m), 926
(m), 847 (vs), 835 (s), 822 (m), 808 (s), 799 (m), 772 (m), 760 (m),
721 (m), 708 (m), 681 (m), 660 (w), 644 (m), 577 (m), 536 (m),
509 (m) cm–1. MS-ESI-EM: calcd. for [M + H]+ 339.1851; found
339.1848. UV/Vis (THF): λ (ν, cm–1; ε, –1 cm–1) = 343 (29155,
˜
(Carom.), 143.3 (Cipso), 182.4, 184.5 (C=N) ppm. IR: ν = 3262 (w),
˜
72300), 328 (30488, 49000), 314 (sh.; 31847, 24700), 276 (36232,
3215 (w), 2976 (m), 2932 (w), 2872 (w), 2361 (w), 2342 (w), 1693
(w), 1665 (s), 1641 (w), 1541 (vs), 1516 (m), 1474 (m), 1462 (m),
1447 (m), 1395 (m), 1379 (m), 1369 (m), 1342 (m), 1317 (vs), 1277
(w), 1248 (m), 1225 (m), 1200 (m), 1144 (s), 1123 (m), 1078 (m),
1049 (s), 1018 (w), 968 (m), 957 (m), 937 (m), 918 (m), 903 (m),
885 (m), 839 (m), 820 (s), 812 (s), 764 (m), 754 (w), 739 (m), 708
(m), 692 (w), 667 (w), 656 (w), 642 (w), 617 (w), 596 (w), 579 (w),
571 (w) cm–1. MS-ESI-EM: calcd. for [M – TMS + H]+ 357.2107;
found 357.2103.
72600), 266 (37594, 53300) nm. Fluorescence (THF, c = 10–6 ): λ
(ν, cm–1) = 383 (26110), 397 (25189), 432 (23148), 450 (sh., 22222)
˜
nm.
X-ray Crystal Structure Analysis of 3b:[24,25] Formula C24H22N2, M
= 338.44, colourless crystal 0.25ϫ0.15ϫ0.10 mm, a = 8.9136(4) Å,
b = 9.6706(4) Å, c = 20.9122(9) Å, β = 94.607(3)°, V =
1797.80(13) Å3, ρcalcd. = 1.251 gcm–3, µ = 0.561 mm–1, empirical
absorption correction (0.873ՅTՅ0.946), Z = 4, monoclinic, space
group P21/n (No. 14), λ = 1.54178 Å, T = 223(2) K, ω and φ scans,
14250 reflections collected (Ϯh, Ϯk, Ϯl), [(sinθ)/λ] = 0.60 Å–1, 3169
independent (Rint = 0.046) and 2776 observed reflections
[IՆ2σ(I)], 244 refined parameters, R = 0.051, wR2 = 0.140, max.
(min.) residual electron density 0.41 (–0.26) eÅ–3, hydrogen atom
at N2 from difference fourier map, others calculated and refined as
riding atoms.
General Procedure for the Synthesis of Compounds 3: The aryl ha-
lide (10.0 mmol) was dissolved in anhydrous THF (10 mL) in a
Schlenk flask that had been dried and then flushed with argon.
The solution was cooled down to –78 °C and n-butyllithium (1.6 
in n-hexane, 7.8 mL, 11.0 mmol) was added. After stirring for 1 h
at –78 °C, 2,2,3,3-tetramethylsuccinonitrile (1; 1.50 g, 11.0 mmol)
dissolved in anhydrous THF (10 mL) was slowly added. The reac-
tion mixture was stirred at –78 °C for 30 min, warmed to room
temperature and stirred for an additional 2 h. Then, methanol
(20 mL) and water (20 mL) were added. The organic layers were
separated, and the aqueous layer was extracted with dichlorometh-
ane (3ϫ20 mL). The combined organic layers were then dried with
magnesium sulfate, before the solvents were removed in vacuo. The
obtained crude product was purified by column chromatography
(pentane/ethyl acetate, 2:1 + 5% triethylamine).
General Procedure for the Palladium-Catalysed Cross-Coupling Re-
actions with N-Silylated Dihydropyrrolimines: In a dried and argon-
flushed Schlenk tube, palladium acetate (9.0 mg, 4 mol-%), rac-
BINAP (49.8 mg, 8 mol-%), potassium tert-butoxide (145.9 mg,
1.3 equiv.), aryl halide 4 or 6 (10 mmol) and N-silylated dihydropyr-
rolimine 2 (1.1 equiv. per coupling site) were dissolved in dried tolu-
ene (5 mL). The reaction mixture was heated at reflux for 6 h before
being diluted with n-pentane (10 mL) and filtered through Celite,
which was washed with more n-pentane (30 mL). The solvent was
removed under vacuum, and the crude product was purified by
column chromatography.
N-[4-(5-Imino-3,3,4,4-tetramethyl-4,5-dihydro-3H-pyrrol-2-yl)-
phenyl]-N-phenylbenzenamine (3a): From 4-bromo-N,N-diphenyl-
benzenamine (3.24 g, 10.0 mmol), n-butyllithium (6.25 mL,
10.0 mmol) and 1 (1.50 g 11.0 mmol). Yield: 0.89 g (2.3 mmol, N-{3,3,4,4-Tetramethyl-5-[5-(triisopropylsilyl)thiophen-2-yl]-3,4-di-
1
23%), yellow resin, m.p. 104 °C. H NMR (300.13 MHz, CDCl3):
hydropyrrol-2-ylidene}-4-(trifluoromethyl)benzenamine (5b): From
δ = 1.14 (s, 6 H, CH3), 1.31 (s, 6 H), 7.02 (d, 3J = 9.0 Hz, 2 H), 4a (112.5 mg, 0.5 mmol) and 2a (246.9 mg, 0.6 mmol). Purification
3
7.10–7.17 (m, 7 H), 7.28–7.34 (m, 4 H), 7.86 (d, J = 8.4 Hz, 2 H,
by column chromatography (hexane/ethyl acetate, 4:1). Yield:
CHarom.), 8.56 (br. s, 1 H, NH) ppm. 13C NMR (75.47 MHz, 156.0 mg (0.3 mmol, 57%), yellow crystalline solid, m.p. 124 °C.
CDCl3): δ = 22.7, 23.4 (CH3), 54.1, 60.5 (Cquat.), 120.3, 124.6,
125.3, 125.9, 129.7, 130.7 (Carom.), 146.6, 151.4 (Cipso) ppm. IR: ν
1H NMR (399.65 MHz, CDCl3): δ = 1.09 (d, 3J = 7.4 Hz, 18 H,
3
iPrCH3), 1.24 (s, 1 H, CH3), 1.35 (sept., J = 7.3 Hz, 3 H, iPrCH),
˜
Eur. J. Org. Chem. 2009, 2077–2087
© 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjoc.org
2083

E.-U. Würthwein et al.
FULL PAPER
1.41 (s, 6 H, CH3), 7.18 (d, 3J = 8.4 Hz, 2 H), 7.28 (d, J = 3.8 Hz,
1609 (m), 1582 (w), 1562 (m), 1547 (m), 1522 (m), 1506 (m), 1487
(w), 1474 (w), 1458 (w), 1447 (w), 1395 (m), 1381 (m), 1369 (w),
3
2 H), 7.55 (d, 3J = 8.3 Hz, 2 H), 7.87 (d, 3J = 3.7 Hz, 2 H, CHarom.
)
ppm. 13C NMR (75.47 MHz, CDCl3): δ = 11.9 (SiCH), 18.6 1319 (vs), 1275 (m), 1240 (w), 1229 (m), 1200 (w), 1157 (s), 1140
[SiCH(CH3)2], 23.0, 23.8 (CH3), 50.0, 53.6 (Cquat.), 123.3, 125.4, (m), 1115 (vs), 1103 (vs), 1063 (vs), 1013 (m), 961 (w), 926 (w), 907
125.5, 125.6, 133.2, 136.6 (Carom.), 142.0, 145.3, 152.8 (Cipso), 178.2, (w), 870 (m), 847 (vs), 835 (s), 820 (m), 800 (s), 760 (m), 727 (m),
187.9 (C=N) ppm. IR: ν = 2968 (w), 2945 (m), 2891 (w), 2868 (w), 708 (m), 694 (w), 681 (w), 656 (w), 621 (w), 613 (w), 590 (m), 567
˜
2841 (w), 1676 (m), 1611 (m), 1580 (w), 1533 (s), 1503 (m), 1474
(w) cm–1. MS-ESI-EM: calcd. for [M + H]+ 483.2048; found
(m), 1460 (m), 1425 (w), 1393 (w), 1377 (w), 1369 (w), 1323 (vs), 483.2041. C31H25F3N2 (482.54): calcd. C 77.16, H 5.22, N 5.81;
1287 (m), 1252 (w), 1229 (m), 1175 (w), 1157 (s), 1113 (vs), 1103 found C 77.06, H 5.13, N 5.68.
(vs), 1063 (vs), 1015 (m), 997 (s), 980 (m), 959 (w), 939 (w), 932
N-{5-[4-(Diphenylamino)phenyl]-3,3,4,4-tetramethyl-3,4-dihydropyr-
rol-2-ylidene}-4-(trifluoromethyl)benzenamine (5e): From 4a
(112.5 mg, 0.5 mmol) and 2b (249.5 mg, 0.6 mmol). Purification by
column chromatography (hexane/ethyl acetate, 4:1). Yield:
(w), 899 (m), 883 (m), 849 (m), 802 (s), 748 (w), 714 (w), 685 (m),
664 (m), 648 (s), 604 (m), 594 (w), 581 (m), 569 (m) cm–1. MS-ESI-
EM: calcd. for [M + H]+ 521.2628; found 521.2615. UV/Vis (THF):
λ (ν, cm–1; ε, –1 cm–1) = 380 (sh.; 26315, 4700), 332 (30166, 12900)
˜
197.0 mg (0.4 mmol, 67%), yellow crystalline solid, m.p. 131 °C.
nm. C28H39F3N2SSi (520.77): calcd. C 64.58, H 7.55, N 5.38; found
C 64.35, H 7.47, N 5.16.
1H NMR (399.65 MHz, CDCl3): δ = 1.22 (s, 6 H, CH3), 1.37 (s, 6
3
H, CH3), 6.96 (d, J = 8.9 Hz, 2 H), 7.11–7.15 (m, 9 H), 7.29–7.33
X-ray Crystal Structure Analysis of 5b:[24,26] Formula C28H39F3N2-
SSi, M = 520.76, yellow crystal 0.15 ϫ 0.15 ϫ 0.15 mm, a =
10.984(3) Å, b = 22.860(5) Å, c = 12.422(3) Å, β = 113.556(1)°, V
= 2859.3(11) Å3, ρcalcd. = 1.210 gcm–3, µ = 0.193 mm–1, empirical
absorption correction (0.9716ՅTՅ0.9809), Z = 4, monoclinic,
(m, 4 H), 7.52 (d, 3J = 8.3 Hz, 2 H), 7.84 (d, 3J = 9.0 Hz, 2 H,
CHarom.) ppm. 13C NMR (100.40 MHz, CDCl3): δ = 22.9, 23.7
(CH3), 50.3, 53.5 (Cquat.), 119.9, 123.0, 124.8, 125.5 (q, CF3), 126.1,
129.7, 131.3 (Carom.), 146.5, 151.7 (Cipso), 178.5, 193.3 (C=N) ppm.
IR: ν = 3067 (vw), 2972 (vw), 2928 (vw), 2868 (vw), 2359 (vw),
˜
space group P21/a (No. 14), λ = 0.71073 Å, T = 123(2) K, ω scans, 2330 (vw), 1666 (m), 1657 (m), 1609 (m), 1589 (s), 1557 (m), 1512
19210 reflections collected (Ϯh, Ϯk, Ϯl), [(sinθ)/λ] = 0.60 Å–1, 5030
independent (Rint = 0.063) and 4057 observed reflections
[IՆ2σ(I)], 386 refined parameters, R = 0.079, wR2 = 0.180, max.
(min.) residual electron density 0.59 (–0.40) eÅ–3, hydrogen atoms
calculated and refined as riding atoms.
(m), 1487 (s), 1452 (m), 1427 (m), 1395 (m), 1377 (vw), 1369 (vw),
1344 (m), 1319 (vs), 1283 (s), 1263 (m), 1248 (m), 1227 (m), 1194
(s), 1175 (m), 1161 (m), 1153 (m), 1134 (s), 1113 (vs), 1101 (vs),
1080 (m), 1063 (vs), 1026 (m), 1013 (m), 989 (vw), 982 (vw), 966
(vw), 955 (vw), 932 (vw), 880 (m), 851 (s), 831 (m), 808 (s), 783
(m), 756 (s), 698 (vs), 662 (m), 642 (m), 619 (m), 604 (vw), 594 (m),
557 (vw) cm–1. MS-ESI-EM: calcd. for [M + H]+ 526.2465; found
N-(5-Biphenyl)-3,3,4,4-tetramethyl-3,4-dihydropyrrol-2-ylidene-4-
(trifluoromethyl)benzenamine (5c): From 4a (225.0 mg, 1.0 mmol)
and 2c (398.8 mg, 1.1 mmol). Purification by column chromatog-
raphy (pentane/ethyl acetate, 2:1 + 5 % triethylamine). Yield:
269 mg (0.6 mmol, 62 %), yellow solid, m.p. 182 °C. 1H NMR
(400.13 MHz, CDCl3): δ = 1.27 (s, 6 H, CH3), 1.42 (s, 6 H, CH3),
526.2463. UV/Vis (THF): λ (ν, cm–1; ε, –1 cm–1) = 395 (25349,
˜
24100), 292 (34305, 13400) nm. C33H30F3N3 (525.61): calcd. C
75.41, H 5.75, N 7.99; found C 75.48, H 5.88, N 8.01.
4-Bromo-N-{5-[4-(diphenylamino)phenyl]-3,3,4,4-tetramethyl-3,4-di-
hydropyrrol-2-ylidene}benzenamine (5f): From 4b (424.5 mg,
3
7.17 (d, J = 8.0 Hz, 2 H), 7.34–7.42 (m, 4 H), 7.56–7.67 (m, 6 H),
3
8.02 (d, J = 8.8 Hz, 2 H, CHarom.) ppm. 13C NMR (100.61 MHz, 1.5 mmol) and 2b (748.6 mg, 1.7 mmol). Purification by column
CDCl3): δ = 22.8, 23.4 (CH3), 50.2, 53.9 (Cquat.), 122.7, 125.5,
125.5, 127.2, 127.2, 128.2, 129.1, 130.0, 132.2 (Carom.), 139.9, 144.8
chromatography (hexane/ethyl acetate, 4:1). Yield: 587 mg
(1.1 mmol, 72%), yellow crystalline solid, m.p. 152 °C. 1H NMR
(Cipso), 177.9, 194.3 (C=N) ppm. IR: ν = 3028 (vw), 2988 (w), 2934 (399.65 MHz, CDCl3): δ = 1.20 (s, 6 H, CH3), 1.35 (s, 6 H, CH3),
˜
3
(vw), 2874 (vw), 2361 (w), 2338 (w), 1738 (w), 1717 (w), 1659 (m), 6.97 (d, 3J = 9.0 Hz, 2 H), 7.00 (d, J = 8.6 Hz, 2 H) 7.11–7.16 (m,
3
3
1609 (m), 1578 (w), 1560 (m), 1520 (s), 1485 (w), 1476 (m), 1460
(w), 1447 (w), 1406 (w), 1398 (w), 1381 (m), 1371 (m), 1323 (vs), 9.0 Hz, 2 H, CHarom.) ppm. 13C NMR (100.40 MHz, CDCl3): δ =
1310 (s), 1285 (m), 1246 (w), 1231 (m), 1190 (w), 1173 (s), 1163 (s), 22.8, 23.7 (CH3), 50.3, 53.4 (Cquat.), 116.7, 120.1, 124.8, 125.1,
1146 (m), 1119 (vs), 1099 (vs), 1063 (vs), 1007 (m), 980 (w), 955 125.6, 129.7, 131.2, 131.2 (Carom.), 146.6, 149.0, 151.6 (Cipso), 177.8,
(w), 930 (w), 914 (w), 876 (w), 851 (s), 839 (m), 810 (m), 785 (w), 192.7 (C=N) ppm. IR: ν = 3059 (w), 3036 (w), 2982 (w), 2930 (w),
6 H), 7.29–7.33 (m, 4 H), 7.37 (d, J = 8.7 Hz, 2 H), 7.84 (d, J =
˜
772 (m), 756 (m), 745 (s), 698 (s), 671 (m), 660 (w), 642 (w), 635
2870 (w), 2357 (w), 2330 (vw), 1651 (m), 1609 (m), 1587 (s), 1560
(m), 1516 (m), 1503 (s), 1479 (vs), 1450 (m), 1422 (m), 1395 (m),
1373 (w), 1360 (w), 1314 (s), 1292 (s), 1279 (s), 1221 (m), 1190 (s),
(w), 604 (m), 594 (m), 563 (m), 554 (w) cm–1. MS-ESI-EM: calcd.
for [M + H]+ 435.2043; found 435.2052. UV/Vis (THF): λ (ν, cm–1;
˜
ε, –1 cm–1) = 374 (sh.; 26738, 15100), 312 (32051, 45800) nm. 1182 (s), 1171 (m), 1140 (s), 1117 (s), 1072 (s), 1026 (m), 1009 (m),
C27H25F3N2 (434.50): calcd. C 74.64, H 5.80, N 6.45; found C 980 (w), 955 (w), 937 (w), 924 (m), 891 (w), 868 (w), 843 (s), 816
74.53, H 5.89, N 6.24.
(m), 804 (m), 781 (w), 754 (s), 745 (m), 725 (w), 692 (vs), 673 (m),
660 (m), 648 (m), 633 (m), 623 (m), 615 (m), 600 (w), 586 (w),
561 (s) cm–1. MS-ESI-EM: calcd. for [M + H]+ 538.1681; found
N-[3,3,4,4-Tetramethyl-5-(pyren-1-yl)-3,4-dihydropyrrol-2-ylidene]-
4-(trifluoromethyl)benzenamine (5d): From 4a (126.3 mg, 0.6 mmol)
and 2d (298.0 mg, 0.6 mmol). Purification by column chromatog-
raphy (pentane/ethyl acetate, 4:1). Yield: 179.0 mg (0.4 mmol,
65 %), bright yellow crystalline solid, m.p. 190 °C. 1H NMR
(300.13 MHz, CDCl3): δ = 1.30 (s, 6 H, CH3), 1.46 (s, 6 H, CH3),
538.1674. UV/Vis (THF): λ (ν, cm–1; ε, –1 cm–1) = 393 (25445,
˜
29500), 292 (34247, 16400) nm. C32H30BrN3 (536.50): calcd. C
71.64, H 5.64, N 7.83; found C 71.84, H 5.38, N 7.51.
2-Bromo-N-{5-[4-(diphenylamino)phenyl]-3,3,4,4-tetramethyl-3,4-di-
7.20 (d, 3J = 8.2 Hz, 2 H), 7.54 (d, 3J = 8.2 Hz, 2 H), 7.96–8.23 hydropyrrol-2-ylidene}benzenamine (5g): From 4c (282.9 mg,
(m, 9 H, CHarom.) ppm. 13C NMR (75.47 MHz, CDCl3): δ = 22.8, 1.0 mmol) and 2b (498.0 mg, 1.1 mmol). Purification by column
23.5 (CH3), 48.9, 56.8 (Cquat.), 122.3, 123.8, 125.0 (q, CF3), 125.8, chromatography (hexane/ethyl acetate, 4:1). Yield: 391 mg
125.9, 125.9, 126.1, 126.5, 127.2, 128.6, 129.0, 129.5, 130.7, 131.3,
132.4 (Carom.), 152.8, 152.8 (Cipso), 178.1, 198.2 (C=N) ppm. IR: ν
(0.7 mmol, 73 %), yellow solid, m.p. 125 °C. 1 H NMR
(300.13 MHz, CDCl3): δ = 1.27 (s, 6 H, CH3), 1.37 (s, 6 H, CH3),
˜
3
3
4
3
= 3048 (vw), 2968 (w), 2932 (w), 2913 (vw), 2872 (vw), 1670 (m), 6.87 (ddd, J = 8.4 Hz, J = 7.7 Hz, J = 1.5 Hz, 1 H), 6.93 (d, J
2084
www.eurjoc.org
© 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Org. Chem. 2009, 2077–2087

Conformationally Restrained 1,3-Diazabutadienes
3
4
= 9.0 Hz, 2 H), 6.99 (dd, J = 7.8 Hz, J = 1.8 Hz, 1 H) 7.10–7.13
N1-{5-[4-(Diphenylamino)phenyl]-3,3,4,4-tetramethyl-3,4-dihydro-
pyrrol-2-ylidene}-N4,N4-diphenylbenzene-1,4-diamine (5k): From 4g
(162.1 mg, 0.5 mmol) and 2b (249.5 mg, 0.6 mmol). Purification by
column chromatography (pentane/ethyl acetate, 4:1) and recrystalli-
3
4
(m, 6 H), 7.19 (dd, J = 7.8 Hz, J = 1.2 Hz, 1 H) 7.25–7.31 (m, 5
3
4
3
H), 7.51 (dd, J = 8.1 Hz, J = 1.2 Hz, 1 H), 7.80 (d, J = 9.0 Hz,
2 H, CHarom.) ppm. 13C NMR (75.47 MHz, CDCl3): δ = 22.9, 23.7
(CH3), 50.1, 53.7 (Cquat.), 116.4, 120.1, 123.0, 124.1, 124.6, 125.6, sation from dichloromethane. The compound crystallises with one
125.9, 127.4, 129.6, 129.7, 131.2, 132.4 (Carom.), 146.5, 149.2, 151.4
molecule of dichloromethane. Yield: 107 mg (0.1 mmol, 25%), red-
(Cipso), 178.4, 193.1 (C=N) ppm. IR: ν = 3059 (w), 2970 (w), 2928 orange glass-like solid, m.p. 103 °C. 1H NMR (300.13 MHz,
˜
(w), 2866 (w), 2359 (w), 2340 (vw), 2328 (vw), 1736 (w), 1668 (m), CDCl3): δ = 1.20 (s, 6 H, CH3), 1.35 (s, 6 H, CH3), 6.93–7.22 (m,
1611 (m), 1589 (s), 1560 (m), 1503 (s), 1487 (vs), 1460 (s), 1425 (s), 22 H), 7.29–7.33 (m, 4 H), 7.88 (d, 3J = 8.8 Hz, 2 H, CHarom.) ppm.
1393 (m), 1377 (w), 1368 (m), 1341 (m), 1312 (s), 1302 (s), 1285 (s), 13C NMR (75.47 MHz, CDCl3): δ = 22.8, 23.6 (CH3), 50.5, 53.1
1221 (m), 1196 (s), 1184 (s), 1136 (s), 1115 (s), 1076 (m), 1042 (m), (Cquat.), 120.2, 122.1, 123.7, 124.6, 125.1, 125.8, 126.0, 129.7, 131.1
1026 (m), 1003 (m), 991 (w), 976 (w), 962 (w), 928 (m), 901 (w),
876 (w), 839 (m), 824 (m), 814 (m), 781 (w), 760 (s), 746 (vs), 727
(Carom.), 143.8, 145.0, 146.6, 148.2, 151.3 (Cipso), 176.4, 191.9
(C=N) ppm. IR: ν = 3061 (w), 3038 (w), 2967 (w), 2926 (w), 2868
˜
(m), 696 (vs), 675 (m), 665 (m), 652 (m), 640 (m), 627 (m), 617 (m), (vw), 2363 (vw), 2342 (vw), 2326 (vw), 1653 (w), 1585 (s), 1560 (w),
604 (w), 586 (w), 575 (w), 563 (w), 554 (m) cm–1. MS-ESI-EM:
1487 (vs), 1450 (m), 1422 (m), 1393 (m), 1369 (w), 1335 (m), 1312
calcd. for [M + H]+ 538.1681; found 538.1670. C32H30BrN3 (s), 1271 (s), 1225 (m), 1194 (m), 1182 (m), 1169 (m), 1142 (m),
(536.50): calcd. C 71.64, H 5.64, N 7.83; found C 72.01, H 5.76, N
7.48.
1117 (s), 1076 (m), 1028 (w), 1011 (w), 1001 (w), 955 (w), 924 (w),
903 (w), 895 (w), 870 (w), 843 (m), 816 (m), 808 (m), 752 (s), 729
(s), 692 (vs), 671 (m), 644 (w), 637 (m), 621 (m), 615 (m), 594 (w),
557 (m) cm–1. MS-ESI-EM: calcd. for [M + H]+ 625.3326; found
N-{5-[4-(Diphenylamino)phenyl]-3,3,4,4-tetramethyl-3,4-dihydropyr-
rol-2-ylidene}-2,4,6-trimethylbenzenamine (5h): From 4d (199.1 mg,
1.0 mmol) and 2b (498.0 mg, 1.1 mmol). Purification by column
chromatography (pentane/ethyl acetate, 4:1). Yield: 182 mg
625.3331. UV/Vis (THF): λ (ν, cm–1; ε, –1 cm–1) = 386 (25907,
˜
15300), 297 (33670, 20100) nm. C44H40N4 (624.82): calcd. for
C44H40N4·CH2Cl2 C 76.15, H 5.96, N 7.89; found C 76.29, H 5.78,
N 7.67.
1
(0.4 mmol, 36 %), yellow-orange glass-like solid, m.p. 77 °C. H
NMR (300.13 MHz, CDCl3): δ = 1.26 (s, 6 H, CH3), 1.34 (s, 6 H,
CH3), 2.04 (s, 6 H, o-CH3), 2.23 (s, 3 H, p-CH3), 6.79 (s, 2 H), 6.92
X-ray Crystal Structure Analysis of 5k:[24,25] Formula C45H42Cl2N4,
M = 709.73, yellow crystal 0.10ϫ0.10ϫ0.10 mm, a = 9.974(8) Å,
b = 13.488(10) Å, c = 14.836(12) Å, α = 103.34(2)°, β = 98.17(2)°, γ
= 92.92(1)°, V = 1915(2) Å3, ρcalcd. = 1.231 gcm–3, µ = 0.207 mm–1,
empirical absorption correction (0.9697ՅTՅ0.9796), Z = 2, tri-
3
(d, J = 9.0 Hz, 2 H), 7.07–7.12 (m, 6 H), 7.25–7.30 (m, 4 H), 7.74
(d, 3J = 9.0 Hz, 2 H, CHarom.) ppm. 13C NMR (75.47 MHz,
CDCl3): δ = 18.5, 20.9 (mesitylen-CH3), 23.0, 23.6 (CH3), 49.8,
53.4 (Cquat.), 120.3, 124.5, 125.8, 127.1, 128.2, 129.7, 131.0, 131.3
¯
clinic, space group P1 (No. 2), λ = 0.71073 Å, T = 123(2) K, ω
(Carom.), 145.6, 146.7, 151.2 (Cipso), 176.1, 192.1 (C=N) ppm. IR: ν
˜
scans, 12802 reflections collected (Ϯh, Ϯk, Ϯl), [(sinθ)/λ] =
0.60 Å–1, 6624 independent (Rint = 0.045) and 4395 observed reflec-
tions [IՆ2σ(I)], 464 refined parameters, R = 0.090, wR2 = 0.254,
max. (min.) residual electron density 0.67 (–0.78) eÅ–3, hydrogen
atoms calculated and refined as riding atoms.
= 2968 (w), 2911 (w), 2866 (w), 2361 (w), 2342 (w), 2326 (w), 1676
(m), 1609 (w), 1587 (s), 1560 (m), 1520 (m), 1504 (s), 1487 (vs),
1450 (m), 1422 (m), 1393 (m), 1369 (w), 1333 (m), 1310 (s), 1296
(s), 1279 (vs), 1219 (m), 1192 (m), 1182 (m), 1153 (m), 1142 (s),
1117 (s), 1076 (w), 1030 (w), 1011 (w), 980 (w), 961 (w), 924 (w),
899 (w), 847 (m), 752 (s), 733 (w), 716 (w), 694 (vs), 667 (w), 654
(w), 637 (w), 621 (m) cm–1. MS-ESI-EM: calcd. for [M + H]+
500.3060; found 500.3060. C35H37N3 (499.69): calcd. C 84.13, H
7.46, N 8.41; found C 84.42, H 7.62, N 8.16.
N-{5-[4-(Diphenylamino)phenyl]-3,3,4,4-tetramethyl-3,4-dihydropyr-
rol-2-ylidene}pyridin-3-amine (5m): From 4i (158.0 mg, 1.0 mmol)
and 2b (498.0 mg, 1.1 mmol). Purification by column chromatog-
raphy (pentane/ethyl acetate, 2:1 + 5% triethylamine). Yield: 77 mg
1
(0.2 mmol, 16%), orange crystalline solid, m.p. 181 °C. H NMR
N-{5-[4-(Diphenylamino)phenyl]-3,3,4,4-tetramethyl-3,4-dihydropyr-
rol-2-ylidene}-4-phenylbenzenamine (5j): From 4f (116.6 mg,
0.5 mmol) and 2b (249.5 mg, 0.6 mmol). Purification by column
chromatography (hexane/ethyl acetate, 4:1). Yield: 152 mg
(0.3 mmol, 52 %), yellow-brown glass-like solid, m.p. 89 °C. 1H
NMR (399.65 MHz, CDCl3): δ = 1.22 (s, 6 H, CH3), 1.35 (s, 6 H,
CH3), 6.95 (d, 3J = 8.9 Hz, 2 H), 7.07–7.13 (m, 7 H), 7.20–7.29 (m,
(300.13 MHz, CDCl3): δ = 1.22 (s, 6 H, CH3), 1.37 (s, 6 H, CH3),
6.96 (d, 3J = 8.7 Hz, 2 H), 7.07–7.13 (m, 7 H), 7.14 (d, 3J = 8.7 Hz,
3
6 H), 7.20 (dd, 3J = 4.8 Hz, J = 8.1 Hz, 1 H), 7.28–7.33 (m, 4 H),
3
7.48 (dt, J = 8.1 Hz, 4J = 1.5 Hz, 1 H), 7.86 (d, 3J = 9.0 Hz, 2 H),
4
3
8.28 (dd, 3J = 4.8 Hz, J = 1.2 Hz, 1 H), 8.41 (d, J = 2.1 Hz, 1 H,
CHarom.) ppm. 13C NMR (75.47 MHz, CDCl3): δ = 22.9, 23.7
(CH3), 50.4, 53.5 (Cquat.), 119.9, 123.0, 124.8, 125.2, 126.0, 129.7,
130.3, 131.3 (Carom.), 144.7, 145.2, 145.9, 146.4 151.6 (Cipso), 179.2,
3
3
8 H), 7.29–7.33 (m, 4 H), 7.37 (t, J = 7.6 Hz, 2 H), 7.52 (d, J =
3
3
8.4 Hz, 2 H), 7.58 (d, J = 7.2 Hz, 2 H), 7.85 (d, J = 8.9 Hz, 2 H,
CHarom.) ppm. 13C NMR (100.40 MHz, CDCl3): δ = 22.8, 23.6
(CH3), 50.3, 53.2 (Cquat.), 120.1, 123.8, 124.6, 125.7, 125.9,
126.0,126.7, 127.0, 127.7, 128.1, 128.7, 129.7, 131.1, (Carom.), 136.4,
193.2 (C=N) ppm. IR: ν = 3061 (w), 3038 (w), 2982 (w), 2928 (w),
˜
2872 (w), 1647 (m), 1609 (w), 1587 (s), 1568 (w), 1558 (m), 1485
(s), 1450 (m), 1422 (m), 1412 (m), 1395 (m), 1371 (w), 1314 (s),
1296 (m), 1279 (s), 1271 (s), 1225 (m), 1192 (m), 1182 (s), 1155 (w),
1142 (m), 1117 (s), 1074 (m), 1028 (m), 1018 (m), 1003 (w), 978
(w), 959 (w), 943 (w), 928 (m), 893 (w), 864 (w), 841 (m), 831 (m),
799 (m), 781 (w), 754 (s), 745 (s), 725 (w), 712 (m), 692 (vs), 671
(m), 662 (m), 644 (m), 633 (m), 615 (m), 586 (m) cm–1. MS-ESI-
EM: calcd. for [M + H]+ 459.2543; found 459.2545. C44H40N4
(624.82): calcd. for C31H30N4 C 81.19, H 6.59, N 12.22; found C
80.59, H 6.59, N 12.04.
141.4, 146.5, 149.1, 151.3 (Cipso), 177.3, 192.2 (C=N) ppm. IR: ν =
˜
3057 (w), 3030 (w), 2970 (w), 2926 (w), 2868 (vw), 1665 (w), 1587
(s), 1564 (m), 1481 (s), 1450 (m), 1422 (m), 1393 (m), 1377 (w),
1369 (w), 1310 (s), 1296 (s), 1277 (s), 1227 (m), 1192 (m), 1182 (m),
1140 (m), 1117 (s), 1076 (m), 1028 (w), 1007 (w), 926 (w), 872 (w),
845 (m), 810 (m), 754 (s), 731 (m), 716 (w), 694 (vs), 669 (m), 640
(w), 617 (m), 592 (w), 561 (w) cm–1. MS-ESI-EM: calcd. for [M +
H]+ 534.2904; found 534.2886. UV/Vis (THF): λ (ν, cm–1; ε,
˜

–1 cm–1) = 390 (25641, 27300), 291 (34364, 28043) nm. C38H35N3 N1,N4-Bis{5-[4-(diphenylamino)phenyl]-3,3,4,4-tetramethyl-3,4-dihy-
(533.70): calcd. C 85.52, H 6.61, N 7.87; found C 85.15, H 6.55, N
7.61.
dropyrrol-2-ylidene}benzene-1,4-diamine (7a): From 6a (165.0 mg,
0.5 mmol) and 2b (498.0 mg, 1.1 mmol). Purification by column
Eur. J. Org. Chem. 2009, 2077–2087
© 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjoc.org
2085

E.-U. Würthwein et al.
FULL PAPER
chromatography (pentane/ethyl acetate, 2:1 + 5% triethylamine).
(498.0 mg, 1.1 mmol). Purification by column chromatography
(pentane/ethyl acetate, 4:1). The compound crystallises with one
Yield: 107 mg (0.1 mmol, 25 %), orange solid, m.p. 129 °C.
1H NMR (300.13 MHz, CDCl3): δ = 1.19 (s, 12 H, CH3), 1.34 (s, molecule of ethyl acetate. Yield: 151 mg (0.2 mmol, 31%), glassy
3
12 H, CH3), 6.96 (d, J = 9.0 Hz, 4 H), 7.06–7.15 (m, 14 H), 7.25– orange solid, m.p. 249 °C. 1H NMR (400.13 MHz, CDCl3): δ =
7.31 (m, 10 H), 7.85 (d, 3J = 9.0 Hz, 4 H, CHarom.) ppm. 13C NMR 1.22 (s, 12 H, CH3), 1.36 (s, 12 H, CH3), 6.97 (d, 3J = 8.8 Hz, 4
3
(75.47 MHz, CDCl3): δ = 22.8, 23.5 (CH3), 50.34, 53.0 (Cquat.), H), 7.08–7.15 (m, 14 H), 7.20 (d, J = 8.4 Hz, 4 H), 7.27–7.31 (m,
120.3, 123.5, 124.5, 125.8, 126.1, 129.6, 131.0 (Carom.), 145.7, 146.6, 9 H), 7.53 (d, 3J = 8.4 Hz, 4 H), 7.87 (d, 3J = 8.8 Hz, 4 H, CHarom.
)
151.0 (Cipso), 176.2, 191.2 (C=N) ppm. IR: ν = 3059 (w), 3036 (w),
ppm. 13C NMR (100.61 MHz, CDCl3): δ = 22.8, 23.6 (CH3), 50.3,
53.2 (Cquat.), 120.2, 123.7, 124.6, 125.9, 126.7, 129.7, 131.1 (Carom.),
136.7, 146.6, 148.5, 151.3 (Cipso), 177.0, 192.0 (C=N) ppm. IR: ν =
˜
2970 (w), 2926 (w), 2868 (w), 2359 (w), 2336 (w), 1736 (w), 1719
(w), 1684 (w), 1663 (w), 1653 (m), 1609 (w), 1587 (s), 1560 (m),
˜
1506 (s), 1487 (vs), 1450 (m), 1420 (m), 1393 (m), 1369 (m), 1312 3059 (w), 3036 (w), 2970 (w), 2926 (w), 2868 (w), 2361 (w), 2342
(s), 1279 (s), 1227 (m), 1219 (m), 1192 (m), 1182 (m), 1140 (s), 1115 (w), 1736 (w), 1719 (w), 1699 (w), 1666 (m), 1609 (m), 1587 (s),
(s), 1074 (m), 1028 (m), 1013 (w), 1003 (w), 980 (w), 961 (w), 926 1560 (m), 1503 (s), 1485 (vs), 1422 (m), 1393 (m), 1369 (m), 1335
(w), 897 (w), 839 (m), 752 (s), 694 (vs), 669 (m), 638 (m), 617 (m), (m), 1312 (s), 1298 (s), 1279 (s), 1221 (m), 1192 (s), 1182 (m), 1140
586 (w), 571 (m), 565 (m) cm–1. MS-ESI-EM: calcd. for [M + H]+
837.4639; found 837.4651.
(s), 1128 (s), 1117 (s), 1074 (m), 1026 (m), 1003 (m), 980 (w), 959
(w), 926 (w), 899 (w), 870 (w), 839 (m), 797 (m), 781 (m), 752 (s),
721 (w), 694 (vs), 669 (m), 660 (m), 640 (m), 617 (m), 588 (w),
571 (m) cm–1. MS-ESI-EM: calcd. for [M + 2H]2+ 457.2512; found
N,NЈ-Bis(5-biphenyl-4-yl-3,3,4,4-tetramethyl-3,4-dihydropyrrol-2-yl-
idene)thiophene-2,5-diamine (7b): From 6b (241.9 mg, 1.00 mmol)
and 2c (797.7 mg, 2.2 mmol). Purification by column chromatog-
raphy (pentane/ethyl acetate, 4:1). Yield: 35 mg (0.05 mmol, 5%),
457.2535. UV/Vis (THF): λ (ν, cm–1; ε, –1 cm–1) = 388 (25773,
˜
31400), 296 (33784, 37400) nm. C64H60N6 (913.22): calcd. for
C64H60N6·C4H8O2 C 81.57, H 6.85, N 8.39; found C 81.73, H 6.54,
N 8.13.
1
deep red crystalline solid, m.p. 229 °C. H NMR (400.13 MHz,
CDCl3): δ = 1.22 (s, 12 H, CH3), 1.39 (s, 12 H, CH3), 7.05 (s, 2 H,
CHthioph.), 7.23–7.27 (m, 5 H), 7.33–7.35 (m, 4 H), 7.43 (d, 3J =
3
8.4 Hz, 5 H), 8.26 (d, J = 8.4 Hz, 4 H, CHarom.) ppm. 13C NMR
Acknowledgments
(100.61 MHz, CDCl3): δ = 22.9, 23.7 (CH3), 50.3, 53.9 (Cquat.),
124.2, 127.1, 127.3, 128.9, 130.6, 132.8 (Carom.), 139.8, 144.4, 150.5
This work was supported by the Deutsche Forschungsgemeinschaft
(DFG, IRTG Münster–Nagoya, SFB 424) and the Fonds der
Chemischen Industrie, Frankfurt. We would like to thank Prof. Dr.
Bart-Jan Ravoo and Dr. Carlo Fregonese for helping with the fluo-
rescence spectra.
(Cipso), 172.3, 190.2 (C=N) ppm. IR: ν = 3057 (w), 3030 (w), 2965
˜
(m), 2920 (m), 2851 (m), 2361 (m), 2342 (w), 1734 (m), 1719 (w),
1701 (w), 1684 (w), 1647 (m), 1636 (w), 1605 (w), 1560 (m), 1539
(w), 1520 (m), 1506 (s), 1487 (m), 1474 (m), 1464 (m), 1456 (m),
1447 (m), 1437 (m), 1404 (m), 1395 (m), 1369 (m), 1362 (m), 1312
(m), 1300 (m), 1279 (m), 1233 (m), 1217 (m), 1184 (m), 1142 (m),
1117 (s), 1074 (m), 1040 (m), 1026 (m), 1020 (m), 1007 (m), 997
(m), 976 (m), 959 (w), 926 (w), 860 (m), 849 (m), 829 (m), 800 (s),
770 (s), 745 (s), 737 (s), 723 (m), 694 (vs), 669 (m), 648 (m), 627
(m), 611 (w), 588 (w), 571 (m), 561 (m) cm–1. MS-ESI-EM: calcd.
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˜
ε, –1 cm–1) = 462 (21645, 5000), 321 (31152, 20100), 303 (sh.;
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33003, 19000) nm.
N4,N4Ј-Bis(5-biphenyl-4-yl-3,3,4,4-tetramethyl-3,4-dihydropyrrol-
2-ylidene)biphenyl-4,4Ј-diamine (7c): From 6c (203.0 mg, 0.5 mmol)
and 2c (406.7 mg, 1.1 mmol). Purification by column chromatog-
raphy (pentane/ethyl acetate, 4:1). Yield: 40 mg (0.1 mmol, 21%),
orange-brown solid, m.p. 236 °C. H NMR (400.13 MHz, CDCl3):
δ = 1.26 (s, 12 H, CH3), 1.40 (s, 12 H, CH3), 7.22 (d, J = 8.0 Hz,
1
3
4 H), 7.34–7.40 (m, 4 H), 7.44–7.47 (m, 7 H), 7.57–7.65 (m, 12 H),
3
8.04 (d, J = 8.0 Hz, 4 H, CHarom.) ppm. 13C NMR (100.61 MHz,
CDCl3): δ = 22.9, 23.4 (CH3), 50.4, 53.8 (Cquat.), 123.6, 126.8,
127.2, 127.3, 128.2, 129.1, 130.1 (Carom.), 132.7, 136.9, 144.5, 148.3
(Cipso), 176.7, 193.0 (C=N) ppm. IR: ν = 3030 (w), 2922 (s), 2853
˜
(m), 1738 (m), 1665 (m), 1605 (m), 1564 (m), 1528 (s), 1487 (s),
1476 (s), 1449 (m), 1404 (m), 1393 (m), 1377 (m), 1369 (m), 1341
(w), 1315 (m), 1304 (m), 1279 (m), 1260 (m), 1242 (m), 1229 (m),
1206 (m), 1186 (m), 1175 (m), 1140 (m), 1117 (s), 1076 (m), 1042
(m), 1024 (m), 1007 (m), 980 (w), 957 (w), 926 (w), 910 (w), 866
(m), 841 (s), 816 (m), 797 (s), 770 (s), 750 (s), 735 (vs), 719 (m),
694 (s), 665 (w), 656 (w), 642 (w), 606 (w), 579 (w), 571 (w), 555
(m) cm–1. MS-ESI-EM: calcd. for [M + H]+ 731.4108; found
731.4057. UV/Vis (THF): λ (ν, cm–1; ε, –1 cm–1) = 384 (26042,
8400), 297 (33670, 34900) nm.
˜
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7218.
Diphenyl[4-(3,3,4,4-tetramethyl-5-phenylimino-4,5-dihydro-3H-pyr-
rol-2-yl)phenyl]amine (7d): From 6c (203.0 mg, 0.5 mmol) and 2b
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3965–3968.
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© 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Org. Chem. 2009, 2077–2087

Conformationally Restrained 1,3-Diazabutadienes
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tallogr., Sect.
A 2003, 59, 228–234), structure solution
SHELXS-97 (G. M. Sheldrick, Acta Crystallogr., Sect. A 1990,
46, 467–473), structure refinement SHELXL-97 (G. M. Sheld-
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[25]
CCDC-713888 (for 3b), -713889 (for 5b) and -713890 (for 5k)
contain the supplementary crystallographic data for this paper.
These data can be obtained free of charge from The Cambridge
Crystallographic Data Centre via www.ccdc.cam.ac.uk/
data_request/cif.
[26] Intensity data for 5b and 5k were collected at 123 K with a
Rigaku Single Crystal CCD X-ray Diffractometer Saturn 7
with MicroMax 7 with Mo-Kα radiation (λ = 0.71070 Å) and
graphite monochromator. The structure was solved by direct
methods (SHELXS-97) and refined by the full-matrix least-
squares on F2 (SHELXL-97).
Received: January 16, 2009
Published Online: March 10, 2009
[23] J. Jang, J. H. Oh, Adv. Mater. 2003, 15, 977–980.
[24] The data set for 3b was collected with Enraf Nonius CAD4 and
Nonius KappaCCD diffractometers, in case of Mo radiation
Eur. J. Org. Chem. 2009, 2077–2087
© 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjoc.org
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